Each of our TRACTrs is comprised of a tumor antigen-binding domain and a T cell binding domain (CD3), while each of our TRACIrs utilizes a tumor antigen-binding domain linked to a T cell costimulatory CD28 binding domain.
The CD3 and CD28 binding domain is always protected by a domain-optimized peptide mask that is covalently bound to the CD3 or CD28 binding domain by way of a tumor specific cleavable peptide linker.
The mask inhibits T cell binding to the CD3 or CD28 domain, until it is removed at the tumor via tumor specific proteases. To extend the half-life of the TRACTr and TRACIr, an albumin binding domain is attached to one of the domain masks via a tumor cleavable peptide linker. Hence, all masks and the albumin binding domain are removed at the tumor.